Thermoplastic element for protection against corrosion in the thermofusion coupling of a thermoplastic tube

ABSTRACT

It is the object of the present invention a thermoplastic element for the protection against corrosion in the thermofused splicing of a thermoplastic tube to a thermoplastic connection, which element has the shape of a fully thermoplastic tubular sleeve, able to be introduced into a socket mouth formed by the expansion of the tube end, said splice element bearing only one internal diameter and two external diameters which define a cylindrical external portion of larger diameter and a tubular projection which diameter is smaller than the former, and which is introduced into the thermoplastic tube, a lateral wall of the external portion defining a front butt of said thermoplastic element against the end of the thermoplastic tube. Said splicing element also exhibits an auxiliary ring which operates as a reference point for the assembly thereof.

FIELD OF THE INVENTION

The present invention refers to a thermoplastic element for theprotection against corrosion in the thermofused splicing of athermoplastic tube to a thermoplastic connection.

More particularly, the present invention refers to acorrosion-inhibiting thermoplastic element at a thermofused splice of athermoplastic tube consisting of an intermediate metal layer placedbetween two thermoplastic layers, with a thermoplastic connection.

BACKGROUND

At present, joints between thermoplastic tubes and connections areperformed by means of thermofusion joining, whereby during a few secondstube and connection are subject to a temperature in the range of from260 to 270° C. and after the elapsing of the heating time both elementsare joined by introducing the male end of one of them into the femaleopening of the other, with an adequate interference grade between theirfacing superficial layers, and they are fused, i.e. they are transformedinto a single piece through them.

It is highly inadvisable to join tubes bearing a metal layer to theconnections thereof by means of thermofusion, as such joining would onlybe accomplished between the external thermoplastic layer and theconnection wall, the intermediate metal layer edge thus remaininginternally uncovered, whereby water circulating through tubing wouldproduce an oxidising process with the consequent deterioration of themetal layer, which would inevitably result in water leaks and/orcontamination.

On the other hand, even where an abutting supplementary union could bedone between the internal layer of the tube and an internal cylindricalsurface of such connection, a highly resistant section would not bepossible to obtain due to the reduced thickness of said internal layer,which section could not absorb the shearing force which causes bendingof the connection wall upon the expansion due to the pressure of fluidworking at high pressure, which on the other hand is easily absorbed bythe tube without any alteration whatsoever due to the presence of theintermediate metal layer and which would obviously produce breakage ofthis joint and the resulting water-metal contact.

Consequently, connection between tube and any class of connectionrequires from the later to be provided with a tubular pin which istightly inserted into said tube end, around which an externalsnap-fastener is applied in order to tighten same around the pin, thuscreating an airtight joint between the internal thermoplastic layer ofthe tube and said pin. Due to said tubular pin thickness, a noticeablereduction of the tubing internal diameter is produced, giving rise toseveral drawbacks.

Further, this kind of connection is very expensive, not only due to themanufacturing cost of the piece itself but also due to the tools andlabour required for the application thereof.

SUMMARY

It is thence the main object of the present invention the implementationof a termofused splice or joint, under maximum and total safetyconditions, of a thermoplastic tube with a thermoplastic connection, bymeans of a thermoplastic element which may be incorporated to the tubeend through thermofusion before the thermofusing operation of this endinto the corresponding opening of said connection, providing suchthermoplastic tube with a fully thermoplastic new with no metal layer,as through it the three layers end covering is obtained, inhibiting bothinternal and external contact of the metal layer edge with theconnection and thus with water and further, a marked increase of theinternal layer thickness is obtained, providing then a largercross-section at the tube end, between its internal surface and saidmetal layer, which allows for the absorption of said bending stresswhich is normally produced at the joint area due to such connectionexpansion upon the high pressure operation of tubing.

Another object of the present invention is the provision of a clearvisual or touch indication that the thermoplastic element has beenincluded and that the connection to be made will be safe.

Another object of this invention is the application of saidthermoplastic element by means of the same conventional tooling used inany thermofused joint of a thermoplastic tube and connection.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to facilitate understanding of this invention and for a betterappreciation thereof, the thermoplastic element and its incorporation tothe thermoplastic tube has been illustrated as follows, according to oneof its preferred embodiments, wherein:

FIG. 1 shows a longitudinal cut view R-R of FIG. 2 and an exploded viewof the splicing thermoplastic element and the end of tube, beforeattaching one to the other by means of thermofusion;

FIG. 2 is a side elevational view of the splicing element;

FIG. 3 is the same view as in FIG. 1, showing interconnection ofsplicing element and the end of the tube once fused;

FIG. 4 is a schematic view showing the splicing element and the tube endapplied to the corresponding nozzles of a thermofusing machine, duringprior heating stage of the surfaces through which fusing of bothelements is to take place;

FIG. 5 shows a longitudinal section illustrative of fusion between thesplicing element and the tube end, according to FIG. 3;

FIG. 6 is the same as FIG. 5, but showing splicing element after it hasbeen applied and attached by means of thermofusion to the tube end, andready to proceed with the final stage of thermofusion of this tube endto the thermoplastic connection;

FIG. 7 shows behaviour of the element already applied to the tube end,when it is introduced in order to be heated into the correspondingnozzle of a second thermofusing machine, for the end stage of tube toconnection thermofusion;

FIG. 7′ is the same view as in FIG. 7 once the introduction of tube withthe splicing element into the second thermofusing machine is completed;

FIG. 8 shows the end of the tube with the splicing element andconnection once heated, at the beginning of said thermofusion finalstage;

FIG. 8′ is the same view as FIG. 8 once the final thermofusion stage iscompleted;

FIG. 9 is an illustrative sketch from a practical example of how thethermofusion between tube end and abutting splicing element andconnection has been accomplished.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 thermoplastic tube A exhibits a wall with two thermoplasticlayers, an external a and an internal a′, made of, for instance,polypropylene or polyethylene, with an intermediate metal layer a″ madeof, for example, aluminum foil adhered to both faces a and a′,exhibiting, for example, a total wall thickness of 2 mm, i.e. 0.7 mmrepresented by external layer, 1.0 by internal layer and 0.2 byintermediate aluminum foil, both faces being provided with an adhesivecover 0.05 mm thick, all these dimensions being given by way of example.

Splicing element C has been developed as an injection pre-moulded fullythermoplastic tubular sleeve, for example, which diameter is larger thatthat of the tube itself, so that in order to be applied at the tube Aend a socket mouth e, which is obtained by expanding end I of said tubeA, should be previously formed.

It is the purpose to attain said expansion of tube end in a range offrom 10% to 20% of the diameter of intermediate metal layer a″ diameter,for all of the tubing diameters, and up to 15% in the particular case ofan aluminum layer exhibiting the above mentioned dimensions.

This splicing element C which form is substantially that of a tubularsleeve exhibits only one internal diameter and two external diameters,which define a cylindrical external portion c which exhibits arectangular longitudinal section which external diameter is the same asthat of the expanded end I of thermoplastic tube A and which exhibits aside wall P abutting against tube end 2 and a height such that it coversthe three layers of said tube, and a tubular projection c′ whichexternal diameter slightly larger than the internal diameter of expandedend I of tube and an internal diameter which is substantially equal tothe internal diameter of tube A. Interference between said diameters isof from about 0.4 to 0.5 mm.

As regards length of c′ dimensioning thereof has been consideredaccording to a length smaller than that of expanded end I.

It is to be noted that above mentioned drawings illustrate said spliceelement C and a supplementary ring C′, which will be described below, asintegral part thereof, not participating in this application stage ofsplice element C of tube A end, it merely remaining incorporated to thelatter in order to be used at the end of the process of thermofusionbetween said tube and the connection piece in the manner and to the endto be explained below.

External portion c of element C exhibits a rear lateral wall P′ whichwill become tube A new end itself upon completion of the operation ofelement C fastening onto said socket mouth e as shown by FIGS. 3 and 6.

Such fastening will be accomplished by means of the direct andsimultaneous thermofusion of abutting side wall P of element C to thejoint end 2 of both thermoplastic layers a and a′ and from said tubularprojection c′ to said internal thermoplastic layer a′, according to thetypical thermofusion technique, by heating on the one hand said abuttingside wall P, external surface 4 of tubular projection c′ and itsexternal edge 4′, and on the other hand said joint end 2 of tube andinternal socket e internal layer, then introducing said tubularprojection c′ into socket e until said side wall P abuts against saidjoint end 2, all of the above under the required pressure andinterference degree in order to obtain a firm interfusion between facingsurfaces of both elements (FIGS. 4, 5 and 6).

The above described operation may be carried manually using female t andmale t′ nozzles provided on both sides of a first thermofusing machineT-I.

This operation of splice end C heating and subsequently, its applicationto the end of tube A could be carried out manually, maintaining spliceelement C applied on female nozzle t of the thermofusing machine inorder to get a maximum contact between abutting lateral wall P ofexternal portion c of element C, and the respective seat 8 of thisnozzle t, and of external surface 4 of splicing element C against wall 9of female nozzle t and its external edge 4′ against the correspondingback step 9′, in order to be sure that all of the element surface whichis to actively act during the interfusion process with the joint end 2and internal layer a′ but maintaining the internal face of theprojection and the splice element adequately “cold” in order to avoidcollapsing of piece.

On the other hand, on male nozzle t′, internal layer a′ of the wall ofexpanded end I of tube A tightens laterally on a correspondingprojection 10 thereof, and at the same time joint end 2 of tube Atightens at its base, obtaining the heating required for its interfusionwith tubular projection c′ and abutting lateral wall P of splice elementC.

Subsequently, both are removed from the thermofusing machine, in orderto be mutually faced and to gradually introduce element C into mouthsocket e of tube end I, applying said element as if it were a stopperinto a bottle, first forcing entering of tubular projection c′ into tubeA internal wall a′ according to the established interference degree,wherein its external edge 4′ proceeds at the superficial portion of theinternal layer forming a lip 11 which aids in sealing the joint betweenboth walls until abutting wall P of splice element reaches the bottomand fuses against the joint end 2 of the three layers of tube A (FIG.6).

Thus a firm union by thermofusion is obtained between element C and tubeA end which comprises an abutted joint II with both thermoplasticlayers, and which continues with a pin joint III between internal layerof tube A and said tubular projection c′ of element C, virtually wedgedinside same, as illustrated by FIG. 6, such that behaviour of saidelement as an integral part of tube A is assured, with said metal layerfully enclosed by thermoplastic material.

At the same time, tube end is internally reinforced, offering a largerannular section between metal layer a″ and tube internal surface at theunion sector where bending stress is to be present upon tubing workingat high pressure, due to the fact that the connection tends to expand,whereas the tube remains unaffected, because of the contention grantedto its metal layer, as already mentioned.

As may be appreciated from what has been described and illustrated,incorporation of this splice element introduces no reduction of tubeconduit, as the inner diameter of tubular projection c′ is substantiallyequal to tube original internal diameter, and is fully within theexpanded end I thereof (FIG. 6).

It is clear that by the incorporation of this element, tube A end isconformed as a single layer conventional tube, which external andinternal surfaces end at a thermoplastic front which comprises all ofthe wall thickness and, accordingly, may be thermofused within aconnecting piece as per the usual technique, heating said end and theinterior of the corresponding nozzle of the connection and introducingone into the other with an interference extent between its lateralsurfaces as required for the obtention of a sound welding between same,without any risk of its intermediate metal layer being exposed.

According to a preferred embodiment, inclusion within the scope of thisinvention has been contemplated of a control element which uponcompletion of the final stage of the thermofusion process between tubeend, already bearing splice element C, and connection piece B, willprovide a clear physical and external indication that said tube endincorporates said splice element and that this joint is safe, i.e. thereis no risk for water to contact tube metal layer.

Accordingly, and as a supplementary element to the above arrangement, ithas been contemplated the temporary inclusion at splice C of asupplemental ring C′, initially formed as an integral part of saidelement C (FIGS. 1 and 2), shaped as an annular piece incorporated as acollar of larger diameter than said element C and which surrounds sameconcentrically, with an appreciable gap between them, they being joinedonly by a very thin intermediate wall 12 as a membrane arranged at theplace where sweeping by the thermofusing machine nozzle is to takeplace. Said thin intermediate wall 12 thickness is such that suchsweeping may only take place if the thermofusing machine provides anadequate thermofusing temperature. Thence, said auxiliary ring C′ actsas a control of the minimum necessary temperature of the thermofusingmachine nozzle.

This auxiliary ring C′ has an internal diameter which is noticeablylarger than the external diameter of the expanded wall of the tube, suchas to fulfil a second auxiliary function, i.e. as a control of spliceelement C positioning, as we will see hereinbelow.

According to the above, element C is thermofused at the tube end asshown and illustrated by FIGS. 4, 5 and 6, bearing this auxiliary washerC′, which has remained separated around same, wherein thermofusionbetween said splice element and tube is limited to joint end 2 of tubeand stop P of this element C and though this auxiliary ring C′ willreceive some heat, indirectly radiated by splice element and itsproximity to the thermofusing machine mouth socket, it is subject to nostress, as the fusion pressure is exerted only between one and theother, leaving aside this auxiliary ring, as shown by FIG. 4 schematics,wherein respective nozzles t and t′ of the first thermofusing machineT-I employed during this preparatory stage for the heating of the partswhich are to be joined: end I of tube A and element C.

Thus, element C is applied to end of tube bearing said auxiliary ring C′around same, as illustrated by FIG. 6, such that when at the stage ofheating tube end, upon the introduction thereof into nozzle t″ of thesecond thermofusing machine T-II (FIG. 7), at the final stage of theprocess, this auxiliary ring C′ abutts against mouth 13′ of end 13thereof and intermediate wall 12 which joins same to splice C yields,provided temperature of nozzle t″ of thermofusing machine T-II is theadequate one, it ruptures and thus freely slides on the tube easily and,pushed by this end of said nozzle t″, is finally at the distance of tubeA end corresponding to penetration length thereof in the latter (FIG.7′), all in such a way that, upon retrieving tube from this nozzle t″ ofthermofusing machine, this auxiliary ring C′ is applied around itsexpanded end I as a “control”, showing that same bears element C, whichis schematically illustrated by FIG. 8 at the beginning of tubepenetration into female portion b of connection B.

It is clear that this auxiliary ring C′is an accessory means thatprotects operator who may have omitted application of splice elementaccording to the invention, without participating thence in theformation of the new thermoplastic end which seals the union betweenexternal and internal layers caps, over the edge of the aluminium cap.

When carrying out this final stage of thermofusion introducing end oftube A into female part b of connection B, auxiliary ring C′ follows(FIG. 8) until it is virtually applied on socket 14′ of female part b,gradually tightening around said tube wall due to the natural, albeitreduced, expansion produced under the compression stress between bothelements which is required by its forced insertion and also to thenatural outwards creepage of both facing superficial layers 15-16 on theside of element C and tube A and 17 by connection B and as a consequencethereof this auxiliary ring C′ tightens over the material which tends toflow forming the classic external curl 18 which it contains, all ofwhich may be appreciated on FIGS. 8 and 8″.

Lastly, reference must be made to the design adopted for this auxiliaryring C′, depicted by FIGS. 1 and 2, with which it has been the intentionto reduce thickness and amplitude of intermediate wall 12 which joinssame to element C body, providing at the same time a configuration suchthat it contributes in maintaining it away from heat originated from thethermofusing machine at the end of the tube (FIG. 4), thus reducing anypossibility of the degradation thereof.

On the other side, and in order to assure that this auxiliary ring C′ isclearly and easily seen, around union, between tube A and connection B,once thermofusion is completed between both elements thus assuring thatthe coupling element has been applied at the end of the tube, not onlyhas it been provided with an ample diameter, but it has further beenequipped with several cylindrical projections 19 which protrude from theexternal periphery thereof underlining the presence of this washer,providing an easy tactile detection in those cases in which suchdetection is not visually possible. Also, it may be provided withcolours contrasting that of the thermoplastic tube, so as to facilitateits visual detection.

Regarding the above mentioned final stage of the thermofusion processbetween connection B and new end of tube now formed by element C, it hasbeen foreseen the establishment of an axial abutting joint, again bythermofusion, between element and internal step 20′ of connection wall20, incorporating between them melted material which flows into theinterior of the connection as an effect of the interfusion of facinglateral surfaces of the tube wall with splice element included and theconnection wall, as schematically depicted by FIG. 8′ as an attempt tocontain this creepage and thus increase contact pressure between saidsurfaces, reducing size of typical curl 21 formed inside the connectionso it does not protrude within the tubing conduit.

In order to better understand how it is done in the practice, thereferred thermofusion union between the wall of the tube end, includingelement and connection wall, it is included as FIG. 9 depicts areproduction of a sketch from a digital image obtained from a partiallongitudinal section of a sector of said union, where it can be seen thedeformation and creepage of surfaces of either element which aremutually fused, establishing a perfect sealing between them, with theintermediate metal layer of the tube being isolated from any internal orexternal contact.

1. A protection element against corrosion in the thermofused splice of athermoplastic tube (A) which includes an intermediate metal layerbetween two thermoplastic layers, with a thermoplastic connection (B),characterized in that said element has substantially the shape of atubular sleeve fully premoulded on thermoplastic material, to be appliedinto a socket mouth (e) formed by the expansion of the end of saidthermoplastic tube (A), said corrosion-protecting element exhibiting asingle internal diameter and two external diameters which define: anexternal cylindrical portion (c) having a rectangular longitudinalsection and exhibiting a side wall (P) abutting against end (2) ofthermoplastic tube (A), and a tubular projection (c′) which diameter issmaller than that of said external portion (c), to be introduced intosaid socket mouth (e) and having an internal diameter which issubstantially identical to tube (A) internal diameter, said protectionelement being attached to socket mouth (e) of said tube by means ofthermofusion between said abutting lateral wall (P) and the edge of boththermoplastic layers of said tube, and between said tubular projectionand the adjacent portion of the internal layer of the tube, in a stageprevious to the interfusion between tube end and thermoplasticconnection.
 2. The protection element against corrosion according toclaim 1, characterized in that height of abutting side wall of theexternal portion is substantially equal to the thickness of the threelayers of the tube.
 3. The protection element against corrosionaccording to claim 1, characterized in that its internal diameter issubstantially equal to the internal diameter of the thermoplastic tube.4. The protection element against corrosion according to claim 1,characterized in that the socket mouth is expanded 10% to 20% of thediameter of the intermediate metal layer of said tube.
 5. The protectionelement against corrosion according to claim 1, characterized in that italso includes an auxiliary ring, which spatially extends around saidexternal portion of the protection element by way of a collar and whichis joined thereto by means of a thin intermediate wall (12).
 6. Theprotection element against corrosion according to claim 5, characterizedin that said auxiliary ring is provided with a plurality of projectionsextending on the periphery thereof.
 7. The protection element againstcorrosion according to claim 5, characterized in that said thinintermediate wall is dimensioned in such a way that it may only bedetached from the external portion when the thermofusion temperature isas required, acting by way of temperature control of thermofusingmachine T-II nozzle.
 8. The protection element against corrosionaccording to claim 5, characterized in that said auxiliary ring exhibitsa colour which contrasts with that of the thermoplastic tube.